1. Field of the Invention
The present invention relates to a resist composition, especially to a chemically amplified positive resist composition, suitable as a micropatterning material, especially for the VLSI manufacture or for the photomask patterning, which shows a very high alkali dissolution-rate contrast before and after exposure, high sensitivity and high resolution, a reduced Line Edge Roughness, and an outstanding etching resistance upon exposure to a high energy beam; and to a patterning process using the resist composition.
2. Description of the Related Art
In recent years, with a tendency of realizing higher integration and higher speed of LSI, a finer pattern rule has been implemented rapidly. This rapid implementation of a finer pattern rule is based on achievement of higher NA of a projection lens, improvement of resist composition properties, and use of shorter wavelength radiation. Especially use of KrF (248 nm) instead of i line (365 nm), the former has a shorter wavelength than the latter, has brought major changes. For example, mass production of a device under 0.18 micron rule is made possible. In the tendency that resolution and sensitivity of resist compositions become higher, the acid-catalyzed chemically amplified positive resist composition (for example, see Japanese Publication of Examined Application No. 2-27660; and Japanese Publication of Unexamined Application No. 63-27829) has excellent features and thus has become a main resist composition especially for deep-ultraviolet lithography.
The resist compositions for KrF excimer laser have began to be used generally for a 0.3 micron process. The compositions are applying to mass-production under 0.25 micron rule and then now under 0.18 micron rule. Furthermore, examination of a 0.15 micron rule has also been started. In this way, the tendency of realizing a finer pattern rule is accelerated increasingly. It is expected that a design rule should be finer of 0.13 μm or less by shifting to shorter wavelength of from a KrF excimer laser to an ArF excimer laser (193 nm). However, it is hard to use novolak resins and polyvinyl phenol resins which have been used conventionally as a base resin for resist, because they have a quite strong absorption around the wavelength of 193 nm. Then, aliphatic resins such as acrylic resins or cycloolefin resins have been examined to ensure transparency and a required dry etching resistance (for example, see Japanese Publication of Unexamined Application No. 9-73173; Japanese Publication of Unexamined Application No. 10-10739; Japanese Publication of Unexamined Application No. 9-230595; and International Publication No. 97/33198).
Among the above resist compositions, the (meth)acrylic-based resist compositions with high resolution have been examined. As for the (meth)acrylic resins, combination of a (meth)acrylic unit which has methyl adamantane ester as an acid labile group unit and a (meth)acrylic unit which has an ester of a lactone ring as an adhesion group unit has been proposed (for example, see Japanese Publication of Unexamined Application No. 9-90637). Furthermore, norbornyl lactone is proposed as an adhesion group with an enhanced etching resistance (for example, see Japanese Publication of Unexamined Application No. 2000-26446; Japanese Publication of Unexamined Application No. 2000-159758; and Japanese Publication of Unexamined Application No. 2002-371114).
Some important issues to be achieved in ArF lithography are to reduce Line Edge Roughness and residue after development. One of the causes for Line Edge Roughness is swelling at the time of development. Polyhydroxystyrene used for a resist composition for KrF lithography resists swelling because phenol of polyhydroxy styrene is a slightly acidic group and has a moderate alkali solubility. On the other hand, polymers containing a highly hydrophobic alicyclic group tend to swell at the time of development, because the polymers are dissolved with a carboxylic acid with strong acidity.
A naphthalene ring has a weak absorption at the wavelength of 193 nm. Vinylnaphthalene-copolymer-based ArF resist compositions have been proposed (for example, see J. Photopolym. Sci. Technol., Vol. 11, No. 3, p 489 (1998); Japanese Publication of Unexamined Application No. 2004-163877; and Japanese Publication of Unexamined Application No. 2002-107933). Because a naphthalene ring having a hydroxy group is slightly acid like phenol, and it is expected that the compositions are conducive to preventing swell at the time of development. The naphthalene ring also has the advantage of having high etching resistance.
The ArF lithography was partially introduced to fabricate devices of 130 nm node, and has become the main lithography technique to fabricate devices of 90 nm node and 65 nm node. As a next lithography technique to fabricate devices of 45 nm node, 157 nm lithography with F2 laser was initially thought to be promising. However, a delay in developing the lithography technique was pointed out due to problems such as low quality of a CaF2 single crystal used for a projection lens, involvement of design changes of optical systems owing to indispensable use of hard pellicle, and deterioration of etching resistance of resists. Therefore, the ArF liquid immersion lithography has suddenly gathered attention (for example, see Journal of photopolymer Science and Technology Vol. 17, No. 4, p 587 (2004)).
The more numerical aperture (NA) of a projection lens projecting pattern image onto a substrate increases, the more resolution of the lens improves. In the liquid immersion lithography, a gap between a projection lens and a wafer is filled with liquid with a higher index of refraction than that of air to design NA of the projection lens to be 1.0 or more, thus high resolution can be achieved. As for the liquid, water with an index of refraction of 1.4366 is under review.
However, the liquid immersion lithography caused problems that a resist pattern obtained through the liquid immersion exposure and development collapses or becomes T-top profile. Therefore, a patterning process that can provide an excellent resist pattern after development with the liquid immersion lithography has been demanded.